There are already known various constructions of jet engines, among them such capable of powering supersonic airplanes. Renewed interest in high-speed flight ahs revivied interest in advanced high-speed propulsion systems. Studies made by Franciscus, L. C. in Supersonic Through-Flow Fan Engines for Supersonic Cruise Aircraft, NASA TM-78889, 1978 and in The Supersonic Through-flow Turbofan for High Mach Propulsion, AIAA-87-2050 at AIAA/SAE/ASME Joint Propulsion Conference, June 1987; by Trucco, H. in Study of Variable Cycle Engines Equipped With Supersonic Fans, Final Report, (ATL TR 201 Advanced Technology Laboratories, Inc., NAS3-17559), NASA CR-134777, 1975; and by Tavares, T. S. in A Supersonic Fan Equipped Variable Cycle Engine for a Mach 2.7 Supersonic Transport, Final Report for NASA Grant NAG3-697, 1986 have indicated that substantial improvements can be obtained by using a fan that is capable of accepting supersonic flow. The engines investigated in these studies were turbofans in which the supersonic fan replaced the conventional fan, and a supersonic diffuser was located downstream of the fan to provide subsonic flow into the high-pressure compressor. The advantage of this engine is attributed to the improvement in the installed thrust specific fuel consumption and the reduced inlet and nacelle weight. However, this type of powerplant, like the conventional turbofan, is probably limited to flight speeds below approximately Mach 3.5.
There is current interest in cruising at flight speeds in the Mach 5-6 range. At these speeds, a ramjet is an attractive powerplant; however, it cannot take off and accelerate through the low supersonic speed regime. A light-weight engine is needed to accelerate to the cruise condition. Current proposals dealing with this problem involve the use of two types of jet engines, usually in an over/under arrangement, one of them being operated only at subsonic, transonic and low supersonic speeds and the other being a ramjet engine which is activated only at higher supersonic speeds. It will be appreciated that the use of such alternative separate engines each of which is being used to power the airplane only during a certain phase of the flight regime and is idle and thus constitutes excess weight during the respective remaining phase greatly increases the take-off gross weight of the airplane and thus either reduces the payload of the airplane or increases its fuel consumption, or both.
Accordingly, it is a general object of the present invention to avoid the disadvantages of the prior art.
More particularly, it is an ob]ect of the present invention to provide a jet engine for use on an airplane that is to be accelerated to and cruise at high supersonic speeds, which engine does not possess the disadvantages of the known engines of this kind.
Still another object of the present invention is to develop the jet engine of the type here under consideration in such a manner as to be able to power the supersonic airplane throughout its flight regime from subsonic to high supersonic speeds.
It is yet another ob]ect of the present invention to devise an engine of the above type the operation of which can be easily adapted to various flight conditions and particularly velocities and amounts of the incoming air that enters the engine.
A concomitant object of the present invention is design the jet engine of the above type in such a manner as to be relatively simple in construction, inexpensive to manufacture, easy to use, and yet reliable in operation.